In single-plate solid-state image sensing apparatuses, a color filter arrangement is placed on a single image sensing element. In CCD (charge coupled device) image sensing elements, for example, a plurality of photodiodes (PDs) are arranged two-dimensionally, vertical CCDs (VCCDs) are arranged with respect to the vertical columns of these PDs, and one horizontal CCD (HCCD) is coupled to one end of all these VCCDs. The PDs constitute pixels for converting incident light into signal charges corresponding to the light amount. The color filter arrangement includes a plurality of filter units that are arranged two-dimensionally. For example, the plurality of filter units may each be made of a 2×2 arrangement of a first, a second, a third and a fourth color element, and may be arranged on the image sensing element so that those color elements correspond to the respective pixels of the image sensing element. In the color filter arrangement referred to as the Bayer arrangement of primary colors, the first, second, third and fourth color elements have, for example, selective transmissivity for red (R), green (G), green (G) and blue (B), respectively. For convenience, the G's that are flanked by two R's are denoted as “Gr,” whereas the G's that are flanked by two B's are denoted as “Gb.” Furthermore, as a complementary color filter arrangement, a color filter arrangement is known, in which the first, second, third and fourth color elements have selective transmissivity for magenta (Mg), green (G), cyan (Cy) and yellow (Ye).
In recent years, image sensing elements are provided with ever higher numbers of pixels, in order to realize image sensing with ever higher resolutions. At present, digital still cameras (DSCs) equipped with CCD image sensing elements with 2 million pixels or 4 million pixels are on the market, and prototypes of image sensing elements having more than 10 million pixels have been reported.
On the other hand, DSCs are required to provide not only still pictures, but also moving pictures. In the case of still picture image sensing, there are hardly any temporal restrictions after the shutter has been closed, so that it is possible to individually read out the signal charges of all pixels using the VCCDs and the HCCD at a slow pace in case of image sensing elements with large numbers of pixels. But in a monitoring mode for example, in which moving pictures of the object are displayed on a liquid crystal monitor so as to monitor the most suitable moment to take a picture, the maximum driving frequency of the VCCDs and the HCCD is limited by the frequency characteristics of the amplifier that is provided on the output side of the HCCD, and as a result, the frame rate of moving pictures decreases as the number of pixels of the imaging element increases.
To address this problem, the technique disclosed in JP 2000-209599A (publication date: 28 Jul. 2000) proposes that in the monitoring mode, for every three columns, the transfer of signal charges from the VCCDs to the HCCD is prohibited for two columns. Thus, the signal charges of the pixels of two columns are discarded for every three columns, and as a result, the frame rate can be increased. It is furthermore known to increase the frame rate by discarding the signal charges of pixels of two rows for every three rows in the VCCDs. Furthermore, as long as filter units made of 2×2 arrangements of color elements are adopted, the desired color information can be obtained from the remaining signal charges that have not been discarded.
However, employing a technique of selectively discarding signal charges of pixels as described above worsens the light utilization efficiency, and there is the problem that it is in particular not suitable for image sensing at low illumination. Moreover, if the signal charges of pixels are discarded for only rows or only columns, then the spatial frequency characteristics in the vertical direction or the horizontal direction become unbalanced, and as a result, the image quality becomes poor.